Allowance for Credit Losses - Accrued Interest Receivables (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 291	$ 291
Allowance for credit losses	3	3
Accrued interest receivables, net	288	288
Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	156	156
Charge-off of accrued interest receivables	3	4
Securities Held-to-maturity [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	29	29
Other Financial Assets Measured at Amortized Cost [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	1	1
Securities available-for-sale [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 105	$ 105